Preheat oven to 350°F and prep a standard muffin tin with cupcake liners or by greasing each well.
Sift the cocoa powder into a large bowl. Add the hot coffee (or hot water) and whisk until the cocoa powder dissolves. Set aside to cool slightly.
In a medium sized bowl, sift together the flour, baking powder, baking soda, salt, and cornstarch. Stir so that ingredients are evenly distributed and set aside.
In the large bowl with the cocoa powder and coffee, add the granulated sugar and stir to combine.
Add eggs, vanilla, milk, and melted butter to the cocoa powder mixture. Whisk until fully mixed.
Whisk the dry ingredients into the wet ingredients until all flour is just combined.
Scoop the batter into the prepared muffin tin. Each well of the muffin tin should be about ¾ full with batter. There may be excess batter when using a standard muffin tin - do not overfill.
Bake at 350°F for 24-26 minutes, or until a tester inserted into the center of a cupcake comes out clean.
Let cool before frosting. Enjoy!